Method and apparatus for measuring and controlling the constituent potentials of gases



Jan. 8, 1963 J. J. TONEY 3,072,792

METHOD AND APPARATUS FOR MEASURING AND CONTROLLING THE CONSTITUENT POTENTIALS 0F GASES Filed Aug. 13, 1958 ill-- PECORD/NG '0 CONTROLLER POSITION CON TIZOLLER GAS IN VEN TOR.

ATTORNEY Patented Jan. 8, 1963 3,072,792 METHOD AND APPARATUS FOR MEASURING AND CONTROLLENG THE CONSTITUENT POTENTIALS F GASES John J. Torrey, South Holland, Ill., assignor to Sunbeam Corporation, Chicago, IlL, a corporation of Illinois Filed Aug. 13, 1958, Ser. No. 754,808 8 Claims. (Cl. 25083.6)

The present invention relates to methods and apparatus for measuring and controlling the constituent potentials of gases, and more particularly relates to method and apparatus for controlling the carbon potential of heat treating or carburizing furnaces and exothermic or endothermic gas generators.

There are various processes in which certain constituent potentials of gases, liquids or solids must be controlled and the present invention is particularly concerned with methods and apparatus for determining such potentials. One such process or group of processes in which constituent potentials must be determined is used in the heat treating of tool steel to add, for example, a predetermined amount of carbon to the casings of tool steel articles, and the present invention is described in connection with a carburizing furnace. It will be understood by those skilled in the art that the principles of the invention which are described for use in measuring the carbon potential of a gas may also be used for measuring the potentials or pressures of other elements.

In carburizing articles formed of tool steel, the articles are usually heated in a furnace containing a gas which has a carbon potential below, in equilibrium with, or exceeding that of the articles. Accordingly, under reducing conditions carbon is transferred from the gas to the articles and the amount of carbon which is so transferred is dependent to a large extent upon two factors. One of these factors is the carbon potential difference between the articles and the gas, and the other is the length of time that the articles are kept in the furnace. Both of these factors must, therefore, be controlled, and this may be accomplished either by maintaining them independently constant with respect to fixed reference values or by maintaining the product of the two at a constant value, while permitting some variations in their absolute values. However, irrespective of the manner in which these factors are controlled, it is necessary to measure the carbon potential of the furnace gas, and it is desirable that this measurement be precise and that it be made continuously to insure accurate control at all times of the amount of carbon transferred to the articles.

Therefore, a principal object of the present invention is to provide a new and improved method of determining constituent potential.

Another object of this invention is to provide new and improved apparatus for carrying out this method.

Still another object of the present invention is to provide a new and improved method of determining the carbon potential of a gas.

A further object of the present invention is to provide new and improved apparatus for controlling the carbon potential of the atmosphere in a heat treating furnace.

Briefly, the above and further objects of the present invention are realized in accordance with the present invention by reacting at least a portion of the material to be tested with a reference material having one or more radioactive constituents which are transferable to the test material during the reaction process, and thereafter measuring the radioactivity of either the reference material or the test material to ascertain the amount of radioactive constituents which were transferred from one mate rial to the other during the reaction process.

In a particular embodiment of the invention, the carbon potential of the gas in a carburizing furnace is determined by passing a continuous sample of the furnace gas over the surface of a non-gaseous reference material including a known amount of radioactive carbon and having a carbon potential exceeding that of the furnace gas. The passage of the gas over the reference material results in the transference lfIOl'Il the reference material to the sample of an amount of radioactive carbon which depends upon the difference in value of the carbon potential of the gas and that of the sample. Following the reaction of the gas with the reference material, the radioactivity of the gas is measured to provide an indication of the amount of radioactive carbon which was transferred thereto and thus permits the calculation of the carbon potential of the furnace gas.

In accordance with another embodiment of this invention, the carbon potential of the gas is determined by measuring the radioactivity of the reference material after the reaction thereof with the furnace gas.

The invention, both as to its organization and operation, together with further objects and advantages thereof, will best be understood by reference to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of one embodiment of the present invention;

I FIG. 2 is a schematic illustration of another embodiment of a portion of the system shown in FIG. 1; and

. FIG. 3 is still another embodiment of a portion of the system shown in FIG. 1.

Referring now to the drawings, and particularly to FIG. 1 thereof, there is shown a heat treating furnace 10 having a gaseous atmosphere therein which is under the control of an electrically operated gas generator 11. The generator 11 emits a gas having controlled amounts of certain desired constituents, and, for example, where the furnace 10 is used for carburizing the casings of steel articles, the gas generator 11 may emit a gas containing controlled amounts of carbon monoxide, hydrogen, nitrogen and water vapor and may have a carbon potential up to .95. A plurality of articles 12 to be carburized may be supported in the furnace 10 on a conveyor belt 13 which is driven by a suitable electric motor 14 so as to move the articles 12 through the furnace 10 at a predetermined rate of speed. Accordingly, by maintaining an atmosphere having a constant carbon potential in the furnace 10, the speed of the motor 14 may be regulated to control the amount of carbon which is absorbed from the furnace gas by the articles 12. Alternatively, the rate of speed of the conveyor 13 may be held constant and the carbon potential of the furnace gas may be adjusted to control the carbon content of the treated articles. Although either of these methods may be used, in order to facilitate an understanding of the present invention, the system of FIG. 1 employs a speed regulated motor 14 and control means for maintaining the carbon potential of the furnace gas constant.

Gas generators which are suitable for use in the system of the present invention are commercially available and well known in the art and generally include a vertically disposed tubular retort 16 filled with brick cubes 17 impregnated with nickel or some other suitable catalyst. The retort 16 is heated by any suitable means to the cracking temperature and a mixture of propane, methane, or the like, and air is forced through the retort 16 by a pump 18. As the gas passes through the hot retort 16 it is cracked to produce a gaseous mixture having the desired constituents, and the density. of these constituents varies with the ratio of air to gas which is supplied to the retort 16 by a motor operated ratio control valve 19.

In order to control the adjustment of the va1ve'19 in accordance with the carbon potential of the furnace gas so as to maintain this potential constant, means are pro vided in accordance with the present invention for measuring the carbon potential of the furnace gas and for producing an electric signal which is indicative of this meas urement and which is suitable for operating a recording controller 20 and a position controller 21 which cooperate to provide a record with respect to time of the carbon potential of the furnace gas and to adjust the valve 19 in such a manner as to regulate the carbon potential of the furnace gas.

As shown, an apertured probe 22 extends into the furnace at a location substantially displaced from the gas inlet so as to extract a typical sample of furnace gas rather than a sample of the gas as supplied directly from the generator 11. Under certain circumstances it might be desirable to measure the carbon potential of the gas as initially supplied to the furnace and in that case the probe 22 would be more proximately located with respect to the gas inlet. However, in either case the probe 22 should be properly located to extract a gaseous sample having a temperature in the carburizing range.

A reference material in the form of a strip of wire or ribbon 23 is disposed in the probe 22 in close proximity to the aperture 22 therein so that the sample of furnace gas which is sucked into the probe 22 by a pump 24 passes over the surface thereof. The strip 23 has a known carbon potential exceeding that of the furnace gas and is at least partially located in the furnace 10 so as to be heated to the proper value whereby some of the carbon is released from the strip 23 to the sample as the hot gas passes over it. Preferably, the strip 23 is an ironcarbon alloy with a substantial portion of the carbon being constituted by carbon 14. Consequently, some of the carbon which is released to the sample is carbon 14-, which being radioactive can be detected by any suitable beta ray sensing device, the amount of beta rays or other radioactivity thus measured being a precise indication of the relative carbon potentials of the strip 23 and the sample.

In order to measure the radioactivity or beta emission from the sample after it has reacted with the strip 23, a flow type ionization chamber 25 is connected between the pump 24 and the probe 22. As shown, the ionization chamber 25 is conventional in construction and includes an outer cylindrical electrode 26 and an inner electrode 27 which is insulated from the outer cylinder 26. The cylinder 26 is maintained at an adjustable predetermined potential by means of a battery 28 which is serially connected with an adjustable resistor 29 between ground and the cylinder 26. The inner electrode 27 is connected to ground through the series connection of a pair of resistors 32 and 33. As the sample of furnace gas including the radioactive carbon passes through the ionization chamber 25, a current flows between the electrodes 26 and 27 and develops across the resistor 33 a unidirectional voltage which is proportional to the amount of carbon 14 contained in the sample being passed through the chamber 25.

The unidirectional voltage which is thus developed across the resistor 33 is converted into a fixed frequency AC. voltage by a vibrating reed electrometer or capacitive commutator 36. The commutator 36 comprises a vibratable plate 35 which is connected to the junction of the resistors 32 and 33, and a stationary plate 37 which is connected to ground through an RF bypass capacitor 38. The plate 35 is caused to vibrate at a fixed frequency by a buzzer type circuit including a battery 45, a solenoid 46 and a carbon button 48 connected in series. Energization of the solenoid 46 attracts the plate 35 which in turn compresses the button 48 to increase its resistance and thus to decrease the energization current through the solenoid 46.

The potential of the plate 37 is adjustable by means of a potentiometer 40 which is connected between ground and the positive terminal of the battery 28. The plate 35 is connected to the control grid of a pentode amplifier 42 by means of a capacitor 43. A conventional grid leak resistor 44 is connected between the control electrode of the tube 42 and ground to prevent the building up of a charge on that grid. The AC. output signal from the commutator 36 is thus coupled through the capacitor 43 to the control electrode of the tube 42 wherein it is amplified and supplied to the recording controller or recorder 20. The recorder 20 is calibrated to indicate the carbon potential of the furnace gas being measured and, in addition, provides an output control voltage signal which is coupled to the position controller 21 through a conductor 50. The signal thus supplied to the controller 21 is proportional to the carbon potential of the furnace gas and causes the ratio control valve 19 to be so operated as to return the carbon potential of the furnace gas to the desired level.

In order to maintain a constant amount of radioactive carbon available for reaction with the gas sample which is drawn through the probe 22 from the furnace It), the radioactive reference material is in the form of an elongated wire or ribbon 23 which is passed through the probe 22 over a pulley 51 at a constant speed by means of a conventional pinch roller 53 driven by a suitable electric motor 54-. The strip 23 is thus transferred from a supply reel 55 to a take-up reel 56, and as it passes through the probe 22 it is reacted with the hot furnace gas. As indicated hereinbefore, the strip 23 comprises a sufficient percentage of carbon such that its carbon potential is substantially greater than the maximum carbon potential of the furnace gas so as to provide control of the carbon potential of the furnace gas in both an increasing and decreasing direction. For example, the strip 23 may be an iron-carbon alloy including 1% carbon.

In order to minimize the number of times that the supply of ribbon must be replaced, the reel 55 should be relatively large, and it has been found that one pound of ribbon having a quantity of carbon 14 sufficient to provide a radioactivity of 20 millicuries is suflicient for a twelve or thirteen weeks supply of the reference ribbon when the strip is drawn through the probe 22 at a rate of ten feet per hour. This rate of speed is sufiiciently fast to provide accurate control of the furnace gas while enabling sufiicient time for it to be heated to the carburizing temperature as it is drawn through the probe 22.

As indicated above, the time duration during which the articles '12 remain in the furnace 10 is one of two readily controllable factors determining the amount of carbon absorbed by the articles. If this duration of time is decreased, the carbon potential of the furnace gas must be increased to produce a constant carburizing effect on the articles. Accordingly, under some circumstances it may be desirable to synchronize the speed of rotation of the motor 54 with that of the motor 14 so that should the motor 14 increase in speed, because, for example, of an increase in line voltage, the reference strip 23 is also drawn at an increased rate of speed through the probe 22 thus giving the apparent indication that the carbon potential of the furnace gas has decreased. Accordingly, the signal supplied to the position controller 21 will increase thus indicating that the carbon potential of the gas should be increased and resulting in an adjustment of the valve 19 to increase the ratio of gas to air. A fixed effect on the articles is thus provided even though the speed of the motor 14 is not regulated.

Referring now to FIG. 2, there is shown an alternative embodiment of a portion of the system of FIG. 1. In the arrangement of FIG. 2 there is provided an aperturcd probe 60 for disposition within the furnace Whose gas is to be controlled. The probe 60 houses a storage reel 61, a take-up reel 62, and a pulley 63 disposed opposite an aperture 64 in the end of the probe 60 so that the furnace gas which is drawn from the furnace by the operation of a pump 65 passes over the surface of the reference strip 66 as it is pulled from the storage reel 61 to the take-up reel 62 by the operation of a pinch roller mechanism 67 driven by a motor 68. A Geiger counter tube or Geiger-Miiller counter tube 70 is disposed within the probe housing 60 in such position that the strip 66 passes over the window portion thereof prior to its being wound on a take-up spool 62. Accordingly, the Geiger counter is used to measure the radioactivity of the strip 66 after it has been reacted with the sample of furnace gas which is thus drawn through the probe, and since the strip 66 originally had a predetermined amount of carbon 14 therein so that the number of beta rays originally emitted thereby is accurately known, the beta rays intercepted and measured by the counter 70 is indicative of the amount of carbon 14 which has been released by the strip 66 and therefore is indicative of the difference in carbon potential between that of the strip 66 and the sample of furnace gas. The electrical output of the counter 70 may be supplied to an amplifier tube such as the tube 42 in the circuit of FIG. 1 for amplification and application to a recording controller 20 and a position controller 21 to maintain a constant carbon potential atmosphere in the furnace 10.

Referring to FIG. 3, there is shown another embodiment of the invention for determining the change in carbon content of a reference strip 75 which is drawn from a storage reel 76 to a take-up reel 77 by means of a pinch roller 78 driven by a motor 79. As in the embodiments of FIGS. 1 and 2, the strip 75 is disposed within an apertured probe 80 through which a sample of the furnace gas is drawn by means of a pump 81. After the strip 75 has been reacted with the sample of furnace gas, it is passed through a suitable acid bath 82 maintained in a closed container 83 prior to its being wound on the take-up spool 77. As the strip 75 passes through the acid bath, the carbon within the strip 75 is released as a gas and may be pumped by means of a ptunp 84 from the container 82 to any suitable beta ray sensing device 85 for producing an electrical output which may be used for recording the carbon potentials of the furnace gas and for controlling the operation of the gas generator 15. The beta ray sensing device 85 may be a Geiger counter, a Geiger-Muller counter or it may be the same ionization chamber 25 and electrometer 36 used in the system of FIG. 1.

While certain advantages may be derived by the use of the embodiment of the invention shown in FIG. 3, a disadvantage of this arrangement over that of FIGS. 1 and 2 is that all of the carbon 14 contained in the strip 75 is released in the form of a gas, whereas, in the embodiments of FIGS. 1 and 2 only that carbon 14 which has been released to the sample of furnace gas is lost. Accordingly, with the embodiments of FIGS. 1 and 2, the reference strip may be re-refined to save the expensive carbon 14.

While particular embodiments of the invention have been shown, it will be understood, of course, that the invention is not limited thereto, since many modifications may be made, and it is, therefore, contemplated by the appended claims to cover any such modifications as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. The method of controlling the carbon potential of an atmosphere, comprising the steps of continuously sampling a portion of said atmosphere, reacting said portion with a material including radioactive carbon and having a carbon potential which is substantially greater than the desired carbon potentional of said atmosphere,

then detecting the degree of radioactivity of the sample, and thereafter adjusting the relative percentages of the constituents of said atmosphere to maintain said degree of radioactivity constant.

2. Apparatus for determining a constituent potential of a gas, comprising a housing, a support in said housing for holding a reference material, said material including a substantial amount of said constituent which is radioactive, means for directing said gas onto said reference material to eifect a reaction whereby a transfer of said constituent between said gas and said material occurs if the respective constituent potentials thereof difler, a radioactivity sensing and measuring device, and means for supplying said gas to said device following said reaction.

3. Apparatus for determining the carbon potential of a furnace atmosphere, comprising a reference metal, said metal comprising a substantial amount of radioactive carbon, means for continuously extracting a sample of said atmosphere from said furnace, means for passing said sample atmosphere over the surface of said metal, and means for detecting the radioactivity of said sample atmosphere after it has passed over said surface.

4. Apparatus as set forth in claim 3 which further includes means for continuously renewing the portion of said metal over which said sample atmosphere is passed, whereby the eifective carbon potential of said metal re mains substantially constant.

5. Apparatus for controlling the carbon potential of a furnace gas, comprising means for supplying said gas to said furnace, means for continuously extracting a sample of said gas from said furnace, means for continuously determining the carbon potential of said sampie to produce an electric output signal indicative of said potential, and means responsive to said signal for adjusting said supply means in accordance with the carbon potential of said sample.

6. Apparatus for determining the carbon potential of the atmosphere in a furnace, comprising a tubular probe disposed in said furnace and including an apertured portion in communication with said atmosphere, means for drawing a strip of metal including radioactive carbon through said tube past said aperture, a passageway interconnected between said probe and said device, and means for exhausting a portion of said atmosphere through said probe and said sensing device, rendering the exhausted atmosphere radioactive in proportion to the difference between its carbon potential and that of said atmosphere as it passes over said strip, and a beta ray sensing device connected to sense the beta emission therefrom.

7. Apparatus for determining the carbon potential of the gas in a furnace, comprising a tubular probe at least partly disposed in said furnace, said probe having an aperture at one end of admitting gas into said probe, means for moving a strip of reference material through the portion of said probe disposed in said furnace, said reference material having a carbon potential exceeding that of said gas and including radioactive carbon, beta ray sensing means, means for drawing gas from said furnace past said material and thence to said sensing means, and means responsive to the output of said sensing means for indicating the carbon potential of said gas.

8. A method of determining the constituent potential of gas, comprising the steps of reacting said gas with a solid reference material having a constituent potential exceeding that of said gas and including at least a portion of said constituent which is radioactive, and thereafter measuring the radioactivity of said reference material.

References Cited in the file of this patent Cooper, C Tracer Measures Fuel Distribution, Nucleonics, vol. 15, No. 6, June 1957, pp. 136 to 140. 

7. APPARATUS FOR DETERMINING THE CARBON POTENTIAL OF THE GAS IN A FURNACE, COMPRISING A TUBULAR PROBE AT LEAST 